Enhanced ZScreen modulator techniques

ABSTRACT

A method and system for use in conjunction with a push-pull liquid crystal modulator system for creating circularly polarized light of alternating handedness is provided. The method and system comprise a pair of surface mode liquid crystal cells and a driver electrically coupled to the cells. The driver is configured to move an electrical charge using a quenching pulse comprising a relatively brief voltage spike at a beginning of a waveform period. Multiple additional improvements are provided, including reducing the thickness of the LC gap (the distance between cell electrode plates), creating a charge connection or wiring connection to the cell electrodes, employing anti-reflection coating technology, thinner ITO and ITO index matched to the LC material, bonding all possible air to material surfaces, using superior glass, employing more efficient polarizers, and reducing projector blanking time.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/319,688, entitled “Enhanced Zscreen Modulator Techniques”, filed Jan.9, 2009 which is a continuation of U.S. patent application Ser. No.11/430,598, entitled “Enhanced ZScreen Modulator Techniques,” filed May8, 2006, now U.S. Pat. No. 7,747,206 granted Jan. 13, 2009, inventorsMatt Cowan et al., which claims the benefit of U.S. Provisional PatentApplication 60/742,719, entitled “Quenching Pulse Speed Improvement forPush-Pull Modulator,” inventors Lenny Lipton and Matt Cowan, filed Dec.6, 2005, all of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present design relates generally to the art of stereoscopicpolarizing modulators, and more particularly to improvements to theZScreen®, a push-pull surface mode liquid crystal modulator havingenhanced image clarity, dynamic range, transition time, transmission,and other characteristics.

2. Background of the Invention

The present device is an improved version of the push-pull liquidcrystal (LC) modulator described by Lipton et al. in U.S. Pat. No.4,792,850, issued on Dec. 20, 1988, the entirety of which isincorporated herein. Such a device, commonly called the ZScreen®(“Zscreen”), has been manufactured by RealD Inc. (formerlyStereoGraphics Corporation), originally as an on-screen modulator usedwith CRT monitors for the viewing of stereoscopic images. The devicedeveloped into a projection selection device, i.e. a device used toselect between the left and right images of a stereo pair, for which itis better suited due to certain angle-of-view considerations associatedwith directly viewing CRT monitors.

Since the device uses two LC cells, the optical path length is long,namely twice the path length of a device using a single LC part. Adouble path length reduces the device's useful angle of view because theoptical path length modulates the dynamic range or extinctioncharacteristics of the sheet polarizer used with the device as afunction of angle. Light rays emerging from a projection lens in aprojector are of substantially narrower angular range than the angularrange required for a user to directly view a CRT monitor. Hence, thepush-pull modulator is better suited for the projection environment thandirect view.

For a period of about fifteen years the projection ZScreen was used inconjunction with cathode ray tube projectors and later with projectorsmade by various manufacturers incorporating the digital light projectorengine supplied by Texas Instruments. The device has been used forpresentations on up to fifteen foot screens in the automotive industry,for oil and gas exploration, and for other kinds of applications thatrequire enhanced visualization or deal with graphics that are difficultto understand without the help of the depth cue of binocular stereopsis.

The ZScreen product gained wide acceptance not only because of the goodquality of the image but because it was simple to use only oneprojector, unlike conventional stereoscopic projection devices.

The image quality requirements were found to be more demanding for thetheatrical cinema than for industrial visualization. The product hadbeen employed for years in an industrial environment but when used in atheater on a large screen, shortcomings were evident. The image lackedcontrast, the device reduced the sharpness of the content, hadinsufficient dynamic range for good channel isolation, and a number ofother problems had to be addressed in order to create a premiumfilm-going experience for the motion picture audience and contentcreators. In addition to improvements to the ZScreen, issues withanalyzers in the eyewear selection devices needed to be addressed.

The construction of a typical ZScreen device is illustrated in FIG. 1A.The device is made up of a sandwich of linear sheet polarizer 102, an LCsurface mode device or SMD (also known as a pi-cell) 103, and another LCcell 104. Although the electro-optical effect described here isindependent of the parts being in contact, in this application it isbetter to have the parts in intimate contact. Laminating the linearsheet polarizer 102, SMD 103, and LC cell 104 together reduces lightlosses, resulting from index of refraction mismatches and increases thedynamic range of the device. The optical components described arecoplanar. The linear polarizer 102 has an axis 105, which is given bythe double-headed arrow. Similarly, the rub axes of the SMDs have axesdescribed by double-headed arrows, and are orthogonal to each other. TheSMD closest to a sheet polarizer is labeled 103 and its axis is axis106. The second SMD is labeled 104 and its axis is axis 107.

As shown in FIG. 1A, representative light ray 101 first traverses linearpolarizer 102, and then SMDs 103 and 104. The electro-optical effect ofSMDs 103 and 104 is attributed to their behavior and construction, whichrequires an input of polarized light. As noted the rub directions of theSMDs 103 and 104 are orthogonal with respect to each other, and SMDs 103and 104 are bisected by the axis 105 of linear polarizer 102. Therefore,the axis 105 of linear polarizer 102 is at 45 degrees, respectively, toboth SMD parts 103 and 104.

Certain issues exist with an implementation such as that shown in FIG.1A, particularly in the theatrical environment, where extremely highquality projection and viewing requirements exist. Most notably, theprevious ZScreen designs when employed in the theatrical environmentsuffer from inadequate image clarity, low dynamic range, slow transitiontime, poor transmission characteristics, and other performance issues.

The present design seeks to address the performance of the ZScreendevice, and push-pull SMD liquid crystal modulators generally, toincrease the enjoyment of perceiving a stereoscopic image in atheatrical environment. It would be advantageous to offer a design thatenhances or improves the ZScreen, or push-pull surface mode liquidcrystal modulators generally, and in particular a design that offersbenefits over those previously available.

SUMMARY OF THE INVENTION

According to a first aspect of the present design, there is provided apush-pull liquid crystal modulator system for creating circularlypolarized light of alternating handedness comprising a pair of surfacemode liquid crystal cells having orthogonal rub axes, a linear polarizerhaving an absorption axis bisecting the orthogonal rub axes, and adriver electrically coupled to the cells, and capable of driving thecells so that when one cell in the pair is in a higher voltage state,the other cell in the pair is in a lower voltage state. The systemincludes an improvement comprising drive circuitry within the drivercausing the driver to move an electrical charge using a quenching pulsecomprising a relatively brief voltage spike at a beginning of a waveformperiod.

According to a second aspect of the present design, there is provided amethod of displaying a stereoscopic video or digital motion pictureimage. The method comprises positioning a push-pull liquid crystalmodulator that includes a pair of surface mode liquid crystal cells withorthogonal rub axes and a linear polarizer having an absorption axisbisecting the orthogonal rub axes, so that light comprising the imagepropagates therethrough. The method further comprises driving themodulator in synchronization with fields of a field sequential image sothat the transmitted image emerging from the modulator consists ofright-handed circularly polarized fields alternating at the field ratewith left-handed circularly polarized fields, wherein the drivingcomprises moving an electrical charge using a waveform comprising atleast one quenching pulse comprising a relatively brief voltage spike ata beginning of a waveform period.

These and other advantages of the present invention will become apparentto those skilled in the art from the following detailed description ofthe invention and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A shows the ensemble of parts that make up a ZScreen push-pullmodulator;

FIG. 1B illustrates the use of the ZScreen push-pull modulator with aprojector to produce stereoscopic movies;

FIG. 2 shows the prior art drive scheme used for powering a ZScreenpush-pull modulator;

FIG. 3 shows the improved drive scheme employed in the present device;

FIGS. 4A and 4B are cross-sectional illustrations of a SMD, showing theinternal construction and alignment of directors, given un-energized andenergized states respectively;

FIG. 5 illustrates the charging waveform for the cell, showing the speedimprovement from applying an overshoot or quenching pulse on thecharging waveform;

FIG. 6 illustrates the electrical equivalent circuit, showing theelements that affect the rate of charging or discharging the electricfield on the LC; and

FIGS. 7A, 7B, and 7C illustrate the construction of the SMD cells in thepush-pull configuration with particular attention paid to the electrodestructure of the devices, where left views are perspective viewsdelineating the construction of the push-pull devices and adjacent rightviews are cross-sectional.

DETAILED DESCRIPTION OF THE INVENTION

An enhanced ZScreen design comprising various improvements andenhancements, useful for theatrical projection, is provided. Theimprovements and methods used are described below. Taken together, theteachings disclosed combine to form an optically superior device and indeploying these changes a vast improvement can be obtained. Thisdisclosure concentrates on those items that are unique, novel, and notobvious in their execution or application to workers versed in the art.

Operation of the ZScreen Device

The ZScreen device of FIG. 1A shows linear sheet polarizer 102, an LCsurface mode device or SMD 103, and another LC cell 104. With regard toFIG. 1A, in the case of polarized light, the behavior of the electricvector of the light waves is considered. The rays emerging from sheetpolarizer 102 have their electric vector restricted to a plane thatpasses through axis 105. Such light is called linearly polarized light.The SMDs subsequently cause phase shifts to the orthogonal components ofthe linearly polarized light that traverse these components. If the SMDis energized, the SMD is essentially isotropic. When momentarilyde-energized, the SMD is a phase shifting part, and this combination ofstates contributes to the device's functionality.

FIGS. 4A and 4B show the construction of the ZScreen which comprisesSMDs 103 and 104. SMDs are cells made up of LC (liquid crystal) material407 (brackets), several microns thick (typically between 3 and 6microns), enclosed between parallel plates of glass 401. Theinward-facing surfaces of the glass are coated with indium tin oxide(ITO) material 402 (cross-hatched), a transparent conductor. Coated ontop of the ITO layer is a layer of a polyamide dielectric material 403.The dielectric has imposed thereon a rub direction produced by some typeof a buffing wheel. This rub direction produces micro-grooves thatsuggest an alignment to the directors (dashed or short lines at 406 and407) that make up the LC material. These are dipole clumps of moleculesthat provide the crystalline structure of the liquid contained withinthe region of the region 407 bracketed areas.

In FIGS. 4A and 4B, the director alignment layers 406 are given bydiagonal lines at an angle to the surface of the alignment layers 403.The interior directors of the material, given by dashed linesperpendicular to the surface of the cell 408, are called the “bulk.” Inmost common LC devices, the electro-optical effect is attributed to thebulk and the physics of optically activity. In the case of the SMD, theelectro-optical effect is provided by the surface layer, or by thedirectors in close proximity to the director alignment layer, and thephysics of the directors may be described in terms of phase shifting.

For the desired SMD electro-optical effect to occur, an LC fluid havingthe lowest possible birefringence value is employed. The LC fluid has abirefringence in the range of 0.04 to 0.06 and, by way of example, sucha material is Merck Catalog no. ZLI-2359 fluid with a birefringence of0.05 Δn and a positive dielectric anisoptrophy. Such a material is citedby way of example only and the device described is not limited to theuse of this material, but any material exhibiting the beneficialfunctionality described herein may be employed.

As illustrated in FIGS. 4A and 4B, an LC device of this type functionsas a capacitor. The system delivers voltage to the opposing ITO (402)layers, creating a potential difference between the layers. With respectto the electronic driving circuit, the push-pull device comprises twocapacitors.

The SMD is a three state device. When an SMD is unpowered for a longperiod of time, the SMD is not in a functional or operational state. Thetwo states of interest are when the SMD is driven to a high voltage anddriven or relaxed to a low voltage, or in some cases, a zero voltage.Switching between a low and a high voltage causes the SMD to alternatebetween phase shifting and essentially non-phase-shifting states.

FIG. 4A shows the directors or alignment layers 406 with low, orpossibly no, voltage applied. With no voltage applied, the directorsalign themselves according to the rub direction of the directoralignment layers 406 as shown. In this anisotropic state the device hasphase shifting properties. Because the axis of the cell is at 45 degreesto the axis of the linear polarized light, the polarized light'selectric vector is resolved into two components at right angles to eachother. The components undergo a relative phase shift and this shift, ifthe proper value, creates circularly polarized light. On the other hand,when applying a relatively high voltage to the part, substantially allof the directors are perpendicular to the surface of the cell, and thedevice will be in an isotropic state with no phase-shifting properties.In such a case the polarized light is transmitted unaltered.

In FIG. 4B, the result of applying a voltage is shown. As described, thedirectors are aligned in the direction of the electric field, as shownby 406′. Once voltage is applied to ITO layers 402, an electric field isestablished between these capacitor plates. The directors, which aredipoles, line up to follow the lines of force of the field. The part isat this point isotropic and has no phase-shifting capability since allof the directors, surface directors 406′ and bulk directors 407, arealigned and perpendicular to the plane of the surface of the part. Oncethe voltage is removed, the surface directors 406′ revert, as shown inFIG. 4A at 406, and the part is anisotropic or birefringent and hasphase-shifting capability. In other words, the part in this state actsas a retarder. The degree of retardation is determined by the tilt ofthe surface directors 406, which in turn is determined by the voltageapplied.

FIG. 2 illustrates the waveform that has been employed previously fordriving the push-pull modulator. Specifically, this waveform, isdelivered to the indium tin oxide layer of the cells. As noted, thepush-pull device is an ensemble made up of a linear sheet polarizer andtwo SMDs (FIG. 1A), with the SMDs electrically driven out of phase witheach other. The waveform presented here is only one-half of the drivescheme, applied to only one of the two cells. When maximum voltage isapplied to SMD 103, the minimum voltage is applied to SMD 104. But inboth cases the waveform is as shown in FIG. 2.

FIG. 2 shows the time axis labeled “t” with a dotted line, and zero (0)indicates ground or zero-voltage. The voltage (vertical) axis is markedwith a double-headed arrow and labeled “V”. High and low voltages arelabeled H with plus and minus signs and L with plus and minus signs,respectively. The periods in which the voltages are applied are of equalduration and are labeled T, and the drive cycle conceptually occurs infour portions of equal duration labeled A, B, C, and D. Typical voltagesfor H might be between 10 and 20 volts, favoring the higher values.Beyond a certain value there may be no improvement in electro-opticalperformance; below a certain value performance deteriorates. The net DCbias is zero. If the average voltage over time is not zero,electrochemical decomposition or plating of the LC cell occurs, and thedevice performance degrades.

FIG. 2 also shows that the system initially drives one of the two cellsto a high voltage H and the high voltage is at +H for the period A, andthen decreases to a low voltage −L, typically only a few volts, duringperiod B. During period C the system drives the part to −H, and inperiod D to a value of +L. The effect of driving in this manner is todeliver a large voltage, then a lower voltage, then a negative-goinglarge voltage, and then a positive-going low voltage. The high voltageis called the drive voltage. The low voltage is called the bias voltage.When the system applies a high voltage to SMD 103 of FIG. 1A, the systemapplies a low voltage to the other SMD 104. When the system applies ahigh voltage to SMD 104 it applies a low voltage to SMD 103. The systemapplies the waveforms shown in FIG. 2 to SMD 103 as shown and a waveformone quarter of a cycle out of phase to SMD 104.

When the system delivers a maximum voltage during period A, thedirectors 407 are lined up as shown in FIG. 4B. The surface directorsare aligned parallel to the directors 407 in the bulk or perpendicularto the plane of the glass surfaces. The device is not phase shifting inthis mode. However, some small residual birefringence results since thesurface directors 407 may not be perfectly aligned parallel to the bulkdirectors.

When the minimum voltage in period A as shown in FIG. 2 is at plus orminus L volts, the surface directors 406 are tilted as shown in FIG. 4A.FIG. 4A illustrates the orientation of the surface directors 406aligned. The driver applies low or bias voltage L to one of cells whilethe other cell receives the high voltage. The bias voltage L is used totune the tilt angle of the directors at the director alignment layer406. By applying the bias, the system can tune the birefringence of thetotal system and obtain highly precise control over phase shifting. Thepush-pull modulator can be tuned to output circularly polarized light toan exact wavelength value, as will be described more fully. A properlytuned bias voltage L can be set to compensate for the residualbirefringence of the high voltage, H, cell, and in this manner producescircularly polarized light of the correct value.

With regard to FIGS. 1A and 1B, the projector 108 and projection lens109 produce unpolarized light 101 that passes through linear polarizer102 and then through the rest of the SMD ensemble of parts, namely SMDs103 and 104. At this point linearly polarized light, whose axis is givenby line 105, passes through SMD parts 103 and 104. Two operationalstates are considered here: State 1 and State 2.

In State 1, the driver electrically drives SMD 103 to high voltage H andis isotropic having essentially no phase shifting properties. Theunaffected linearly polarized light traversing SMD 103 then enters SMD104 and undergoes a phase shift since SMD 104 is driven to the lowvoltage state, plus or minus L volts. If the value of L is properlychosen the result is circularly polarized light of one handedness for adesired wavelength. SMD 104 is adjusted to operate for the desiredquarter wave phase shift through the proper selection of voltage L.

In State 2, the driver electrically drives SMD 103 to low voltage L andis anisotropic having phase shifting properties. If the value of L isproperly chosen the result is circularly polarized light of onehandedness for a desired wavelength. Because the axis of SMD 103 isorthogonal to that of SMD 104, the circularly polarized light producedhas opposite handedness to that produced in State 1. SMD 103 is adjustedto operate for the desired quarter wave phase shift through the properselection of voltage L. The circularly polarized light produced by SMD103 enters SMD 104 and undergoes little or no phase shift since SMD 104is driven to the high voltage state, H volts. Since SMD 104 isessentially isotropic, the circularly polarized light emerges unaltered.

The bias voltage tunes the amount of phase shifting of either SMD 103 orSMD 104 for State 1 and State 2, and produces significantly precise λ/4retardation. As is understood in the field, chromatic or dispersioneffects with retarders and the resulting phase shifting can generallyonly be optimized for a single wavelength of light—all other wavelengthsare elliptically polarized. Since the present design comprises a systemwith a polarizer and analyzers, as described in FIG. 1B, in combinationwith selection eyewear 117 used by observer 115, the concern is tuningthe birefringence of the parts to match the requirements of theanalyzers in eyewear 117. Eyewear in this arrangement comprises lensesmade up of left and right-handed circular polarizing filters.

Another reason for applying bias voltage plus or minus L, as shown inportions of the waveform B and D, is to compensate for residualbirefringence. One of the characteristics of the SMD is that all of thebirefringence may not be eliminated in the isotropic state, and use oftwo SMDs in conjunction and tuning the birefringence using the biasvoltage can eliminate the residual birefringence and produce anisotropic ensemble. Imperfections in retardation result from alldirectors at the surface layer not obeying the “suggestion” of therubbed polyamide, or in other words the directors do not follow thedirection of rubbing of the rubbed polyamide.

With respect to the operational properties of the modulator, thepush-pull modulator may be considered a variable axis toggling retarder.In the physical embodiment, a linear polarizer provides linearlypolarized light, and two quarter-wave retarders having orthogonal axesare provided. The linear polarizer can be turned on and off at will.Such an arrangement operates as a single sheet retarder toggled through90 degrees with no mechanical parts. Excellent, high-purity circularlypolarized light of a specific wavelength results from turning on and offthe retardation of the SMDs 103 and 104, for light at a givenwavelength.

The vector sum of the phase shifts of the two parts is controlled by thevoltages applied by the system to the parts. The resultant phase shiftis a vector sum of the electric vectors of the electromagnetic waves, inmutually orthogonal planes, that produce plus or minus quarter-waveretardation. This embodiment is superior to rotating a retarder through90 degrees because the user or operator can precisely tune thebirefringence to match the characteristics of the analyzers. Suchprecise tuning is difficult to achieve with conventional sheetretarders.

Those skilled in the art will recognize that a circular polarizer uses aretarder component that can have only one value of retardation, and theZScreen is a device of this type. Certain achromatic polarizer devicescan be optimized for a broader band of the visible spectrum, but theZScreen is of the non-achromatic type. For any non-achromatic circularpolarizer the analyzer (eyewear) retarder components are selected tomatch the wavelength of the circular polarizer(s). The retardationcomponent(s) of the circular polarizer(s) and the circular analyzer(s)having the same value of retardation yield a maximum dynamic range.Extinction exists on either side of the value of quarter-waveretardation because the ellipticity of the polarizer(s) and analyzer(s)match one another since they use the same value for retardation andbehave identically in this respect. So in effect, the circularpolarization system is also an elliptical system on either side of thequarter lambda (wavelength) selected. As used herein, the term “circularpolarization system” or “circular polarization” refers to both circularand elliptical systems, and the term “elliptical” when used hereinencompasses both ellipse form and circular form. In sum, the ZScreen andeyewear analyzers form a system that has maximum dynamic range at onewavelength but analysis continues to take place for light on either sideof the selected wavelength. Were this not the case, the device wouldexhibit a great deal of cross talk.

With reference to FIG. 1B, the push-pull modulator (102, 103, 104) isshown as described in FIG. 1A and may be used to project a motionpicture or video image. The projector 108 provides the image, where lens109 is the projector's lens, by delivering the video signal to theprojector 110 by video source 111. Video source 111 also providessynchronization signal 112 to the electronic drive box 113 that providesthe voltages shown in FIG. 3. The synchronization signal can be receivedfrom projector 110 but sometimes originates from video on a server orsimilar device. The system applies voltages (FIG. 2) to the push-pullmodulator by cables or wires 114. The unpolarized light 101 is subjectedto polarization by linear polarizer 102. The system then subjects theresultant light to the phase changes and thus the production ofalternately left- and right-handed circularly polarized light by SMDs103 and 104 as described herein.

Arrow 118 shows rays of circularly polarized light. The projected lightreflects off of polarization-conserving screen 116, and may be observedby an observer 115 wearing analyzing spectacles 117. The spectacles 117typically include left- and right-handed circular polarizers, onecovering one eye and one covering the other eye.

The system delivers video fields or motion picture frames of alternatingleft and right perspective to projector 108, projected by lens 109, inthe form of unpolarized light 101. Light then traverses the push-pullmodulator. The left and right perspective fields are polarized withalternately produced left and right (or right and left) handedcircularly polarized light. Alternating the fields at a sufficientlyrapid rate produces a generally flicker free stereoscopic effect for theobserver 115. The system projects a train of circularly polarized lightfields whose characteristics are of alternate handedness—one fieldhaving one handedness, such as right handed, the next field having theother handedness, such as left handed. These fields reflect off ofscreen 116.

The result is that the observer 115 wearing analyzing spectacles 117sees a stereoscopic image. The image is presented to observer 115 in thefield-sequential mode, and the required polarization characteristics areimposed on the light by the push-pull modulator.

Circularly polarized light in a projection system is superior toconventional linearly polarized light because it allows for headtipping. Although chromatic shifts and a reduction in dynamic rangeoccur when the user or observer tips his or her head when watching athree-dimensional movie using circularly polarized light for imageselection, the result is superior to that when viewing a linearlypolarized movie. Even large angular head tipping using the designdescribed here does not result in crosstalk. Crosstalk looks to theviewer like a double exposure. Because one uses circularly polarizedlight, with head tipping, there are relatively minor chromatic andextinction changes. On the other hand, when the system uses linearlypolarized light, as is commonly the case, the law of Malus applies. Thelaw of Malus relates the intensity I of linearly polarized lighttransmitted by a linear polarizer to the intensity I₀ of the incidentlinear polarized light, and the angle B between the plane of the axis ofincident polarized light and the plane of the axis of the analyzer, bythe expression:I=I₀ cos ² B  (1)

A small change in the angle B results in a large change in transmission.Accordingly, only a little head-tipping leads to the perception of adouble image when viewing through linear polarizing spectacles. Thepresent design can eliminate crosstalk between the left and right imagesby optimizing the performance of the push-pull modulator. Transitionsbetween polarization states must be relatively rapid using the presentdesign since any dwelling of one polarization state within an unwantedperspective field contributes to crosstalk.

In designing a stereoscopic motion picture projection system, thedesigner accounts for every optical element from the projector to theeyes of the beholder. Issues exist with respect to the projector,projector colorimetry, projector total luminous flux, projectorpolarization state, and the manner in which fields are sequenced. TheZScreen is a critical item in the system but ZScreen performance cannotbe optimized without addressing performance characteristics of the restof the system, such as projection port glass composition, the projectionscreen, and the eyewear. The port glass is preferably not birefringent,but must have high transmission, and generally must not color shift thelight. The screen preferably has good gain, does not produce colorshifts, has even illumination and conserves polarization. The eyewearcircular polarization retarders must generally match their retarderelements and the retardation value set for the ZScreen. Every portion ofthe system is preferably controlled, via altering design parameters, tooptimize the stereoscopic effect.

Improvements to the ZScreen Device

In addition to the drive scheme discussed with reference to FIG. 2,moving charge faster may be accomplished by switching speed improvementssuch as changing the LC material, reducing the thickness of the LC gap(the distance between cell electrode plates), and creating a chargeconnection or wiring connection to the cell electrodes.

Superior anti-reflection coating technology, thinner ITO and ITO indexmatched to the LC material, bonding all possible air to materialsurfaces, using superior glass, employing more efficient polarizers, andreducing projector blanking time may all enhance overall performance andthe viewing experience. Additionally, the system may exhibit improvedextinction ratios for superior left and right channel isolation byimproving the LC formulation, matching the retardation characteristicsof the eyewear analyzers to the ZScreen, providing superior AR coatings,and enhanced bonding components.

Other improvements to the system include enhancements to the thermalmanagement system, since polarizers fade with exposure to flux, usingfade resistance polarizers, increasing the size of area of the parts,and adding a cooling fan. Improvements have been made to colormanagement by exploiting the spectral characteristics of the modulator.

Finally, better extinction or channel isolation and color neutrality maybe exhibited by improving light transmission, linear polarizer opticalquality, and determining the characteristics of the retarder filmcomponent of the analyzers in order to match the eyewear analyzers andthe ZScreen polarizer.

Drive Scheme Enhancement

The first improvement is the drive scheme used to move the charge. Thedevice seeks to improve the speed or response time of the push-pullmodulator by using a “quenching pulse” shown in FIG. 3 at E′. ComparingFIG. 3 with FIG. 2 shows that the only material difference is theaddition of this lower voltage “spike” or quenching pulse added to thelow voltage or bias section of the waveform at B and D, or in FIG. 3 atB′ and D′. The brief downward section of the waveform is responsible forthe speed improvement disclosed and employed herein.

Switching speed is controlled by two factors. The first is the abilityof the LC directors, as described above and depicted in FIGS. 3, 4A, and4B, to physically move into position to provide the desired retardation.Moving the LC directors into position is driven by the electric fieldprovided to the ITO electrodes. The second factor is the time requiredto create the electric field. The LC cell has an inherent capacitanceproportional to the area of the cell, the dielectric constant of the LCmaterial, and inversely proportional to the cell spacing. In the case ofthe SMDs used for the push-pull application, the capacitance can berelatively large—on the order of tenths of a microfarad or greater.Added to this capacitance is the resistivity of the ITO that carries thecharge to make the electric field. Higher resistivity ITO is thinner butgives better cell performance insofar as transmission is concerned, buta reduction in thickness creates series impedance in the charging of theLC cell, and the series resistance controls charging.

The system requires a total charge Q to change the electric field fromthe off state to the on state. Q is defined by:Q=CΔV  (2)where Q is total charge in coulombs, C is the capacitance in farads, andΔV is the change in voltage. Charge movement is impeded by the seriesresistance of the ITO, creating a time constant. Further limiting thecharging time are the limitations on output current from the electronicmodule 113 that powers the push-pull device.

To minimize the time required to charge the LC cell, the system mayapply a larger differential voltage to the cell for a relatively shortperiod of time, as shown in FIG. 3 at E′. Application of a largerdifferential voltage maximizes the rate of charge transfer. Whensufficient charge has been transferred to achieve the required biasvoltage applied to the cell, the system increases the drive voltage tothe bias level sufficient to induce the correct level of birefringence.

FIG. 6 shows the equivalent circuit of the drive module and the LC cell.In this circuit, the cell is represented by cell capacitance 604 and theseries resistance 603. This circuit is charged by the drive waveform 601in series with the source impedance of the drive module. The circuitallows the charging performance of the liquid crystal cell to be modeledand the electric field across the LC material to be predicted. Thus adrive waveform with a quenching pulse more rapidly creates the electricfield necessary to achieve the required switching of the LC.

FIG. 5 shows the charging waveforms (voltage) for a cell ofapproximately 250 square centimeters, and compares the waveforms of theelectric field at the cell with no quenching pulse, a pulse of 3 voltsof overshoot, and a stronger pulse of 6 volts of overshoot. The threeconditions are modeled in FIG. 5. The first condition is the electricfield across the liquid crystal under normal two level charging as shownat graph 501. The time to achieve the desired electric field is manyhundreds of microseconds. The second case at graph 502 shows 3 volts ofovershoot. Three volts of overshoot brings the electric field toequilibrium more quickly, on the order of 250 microseconds. Using a moreextreme overshoot, as shown in graph 503, the electric field attainsequilibrium more quickly, in about 175 microseconds.

Performance may be improved since charge is moved faster by thequenching pulse creating a larger ΔV, thus creating a larger chargingcurrent. The larger charging current reduces the time necessary to movethe total amount of charge (Q) to create the required steady-stateelectric field to hold the LC molecules in the correct orientation toachieve the required birefringence.

The quenching pulse is illustrated in FIG. 3 as E. The quenching pulseapproaches ground or zero voltage, is applied for a short period of timeas shown in FIG. 3. When the system applies a pulse of this nature,performance improvements may be realized, such as halving the transitiontime. One can get more light on the screen and less crosstalk or theleakage of one perspective view into the other, a phenomenon that isperceptually disturbing. The push-pull modulator is used with, typicallybut not exclusively, a DLP (digital light projector). A DLP© using DMD©a (digital micro-mechanical mirror modulator) chips manufactured byTexas instruments is embodied in projectors by Christie, NEC, and Barco,for example. In this disclosure the use of a DLP projector is assumedbut it will be obvious to one of ordinary skill in the art that thedesign taught here is independent of such a construction and otherdevices may be employed with similar results. As used herein, the term“electronic projector” is employed to mean any type of such device witha high field rate, including but not limited to a digital lightprojector or other appropriate light engine.

Because of the nature of the DLP's micro-mechanical mirror modulation,the system may achieve a shorter or even nonexistent blanking period.The blanking period is the housekeeping period used in video signals,and its historical antecedent was the blanking requirement dictated bythe fact that an electron beam must have time to be steered betweenfields. Today, for the DLP projection system, no such housekeeping isrequired. Therefore a blanking period is enforced to ensurecompatibility of a stereoscopic system requiring modulator transitiontime with equipment that requires a blanking period. A short transitiontime provides a bright motion picture image, since the modulationtransition required for changing the states of polarization reducesprojected light output. Moreover, the greatest separation of perspectiveimages that can be achieved is also desirable. When displayed, the leftimage remains in one channel the right image in the other. Since thismultiplexing occurs in the time domain, a rapid transition of thechanging polarization characteristics promotes channel isolation.

Significant light losses may be suffered in the projection of stereopairimages. Not only do the polarizers employed reduce the light, but alsothe duty cycle reduces the light further since each eye is only seeinghalf the available light (minus the switching time). Improving thetransition time of the SMD modulator significantly enhances overallperformance. The switching time duty cycle increases the amount of timethat the image is black or blanked. A stereoscopic moving image isrepeated at some multiple of the capture rate. If, for example, thesystem captures an image at 30 fields per second (video or computerrate) then the image is displayed twice and “interleaved” with the otherperspective image for a total repetition rate of 120 fields per second(fps). If capture is at the film standard of 24 fps, the repetition ratemay increase by a factor of three, or in this case, to a total of 144fps (24 for one eye, 24 for the other, each image repeated andinterleaved three times). All of this switching between fields of theother perspective requires additional push-pull modulator transitionsthat can exacerbate the loss of light inherent in this image selectionscheme. Therefore performance is enhanced by reducing the duration ofthe blanking or transition time since each transition robs requiredlight for reaching the screen and the eyes of the audience members.

Configuration Changes—LC Material and Connection

Adjustments to the LC material and thickness of the LC gap can havebeneficial effects. To increase the switching speed of the device, thegap in the LC cell is decreased, resulting in a thinner layer of LCmaterial. A thinner LC provides faster switching times.

Changing the connection geometry can reduce series resistance andimprove the speed of the parts. The equivalent circuit of the cell showsthe cell as a capacitor 604 with a series impedance 603. The seriesimpedance 603 is made up of the sheet resistivity of the conductive ITOmaterial. As discussed earlier, the time constant of the cell dictatesthe length of time required to charge the cell to the sustaining voltagenecessary to switch the LC material.

The series resistance in the equivalent circuit of the sheet resistanceof the ITO conductive coating is directly proportional to its geometry.The series resistance increases if the sheet is longer than it is wide,and reduces if it is wider than it is long. In this situation,connections are made on the “width” side.

The cell geometry previously employed was square, with electricalconnections to the cell along one edge. A square cell geometry resultsin a series impedance of typically 100 ohms (for 100 ohm per squareITO). The value of this impedance is a significant factor in chargingthe cell to the equilibrated electric field necessary for adequateoperation.

FIGS. 7A through 7C give possible configurations of push-pull design.The three basic designs are shown in both perspective andcross-sectional views. The design illustrated in 7B is moresophisticated than that of FIG. 7A, and FIG. 7C illustrates a highlyefficient approach. The present design is a basic geometry in which thepush-pull device is rectangular and designed to have an aspect ratiodesigned to match the shape of the beam leaving the projector, therebyminimizing area and reducing manufacturing cost. For 100 ohm per squareITO coating, and for example a cell with an aspect ratio of 2:1 (twiceas wide as it is high) the cell impedance doubles to 200 ohms if theelectrical connections are along the short side, and halves to 50 ohmsif they are along the long side.

Having discussed the properties of the constituent SMD LC cell of thepresent design, attention will now be given to the push-pull ensemble oftwo such parts configured to optimize performance.

These teachings use various electrode designs and connection approachesas given in FIGS. 7A through 7C. The cell impedance can be equivalentlymodeled as a capacitor with a series resistor. The liquid crystal is adielectric separator between the separated plates of the SMD, while theresistance of the ITO provides the series resistance. The resistance (R)portion of the cell impedance can be approximated as a single resistor,or in other words the capacitor may be ignored:R=Rs*L/W  (3)where Rs is the sheet resistance value for the ITO, and L and W are thewidth and length of the ITO square. Length is the dimension between thetwo terminals of the cell. The SMD cell is X inches wide and Y inchestall. In most cases, the cell is wider than it is tall—that is, X isgreater than Y.

FIG. 7A shows the currently manufactured push-pull device with aperspective view of the assembly to the left and the cross-sectional TOPVIEW, so labeled, to the right. In this design the terminals to applythe SMD drive voltage are located on opposite ends of the SMD along thenarrower edges. In this configuration,Ra=Rs*L/W=Rs*X/Y  (4)where Ra is the resistance of the new configuration (FIG. 7A) and X isgreater than Y, and X/Y is always greater than 1. The push-pull ensemble701 is shown with back SMD part 702 and front SMD part 703. The exposedITO electrode surface 704 of back SMD part 702, and the exposedelectrode surface 705 of front SMD part 703 faces away from the reader.In the TOP VIEW drawing of FIG. 7A the corresponding parts areidentified with a prime, such as 701′ corresponding to 701. In thisconfiguration electrical connections are made to surfaces 704′ and 705′and the current must travel across the length of the part which hasincreased resistivity because of its greater length.

FIG. 7B shows one improvement to the current SMD wherein the terminalsare located along the wider edges. The push-pull device 706 comprisestwo SMDs that are shown as front SMD 708 and rear SMD 707. Note that thesame labeling scheme is employed wherein the SIDE VIEW labels use theprime designations for corresponding parts. Electrode ledges 709 and 710are now at the short sides of the parts. By placing the terminals alongthe wider edges, this design reduces the overall resistance lowers theeffective series resistance of the cell.Rb=Rs*L/W=Rs*Y/X  (5)where when X is greater than Y, Y/X is always less than 1. For X greaterthan Y, Ra is greater than Rb. In other words, to reduce the ITOresistance of the SMD, it is better to drive the cell from the wideredges, or apply the voltage across the narrow dimension.

FIG. 7C shows a specialized case where two adjacent edges of the cellform one terminal, while the remaining two edges for the other terminal.In this case, the resistance between the two terminals approaches zeroat the two corners where the terminals nearly overlap. The maximumresistance occurs between the remaining two corners. The equation forFIG. 7B provides the upper limit for the resistance in the configurationof FIG. 7C. The push-pull ensemble is denoted by 711, and the “prime”designations are used for the two cross-sectional views to explain theassembly of the parts, namely the TOP VIEW and SIDE VIEWS to the rightof the perspective view of FIG. 7C. Front SMD 713 and rear SMD 712 havecorresponding electrode ledges 715 and 714.

As the capacitance of the SMD is charged and discharged, the non-uniformresistance of the ITO leads to different rates of charge/discharge ofthe capacitor over the area of the SMD. Correspondingly, the electricfield in the capacitor is non-uniform. However, as the capacitance isfully charged/discharged, the SMD reaches equilibrium where the electricfield is uniform throughout the device.

Transmission Enhancements

Anti-reflection (A/R or AR) coating approaches may also be employed. Thecell design inherently has a number of optical interfaces. At eachinterface, potential damage can be caused to the signal throughreflections. Reflections damage the system or hinder performance in twoways. First, they reduce the amount of light that is transmitted throughthe system. Second, they can add a birefringent effect and alter thecharacteristics of the circular polarization outputted by the push-pulldevice, resulting in contamination and cross talk between the left andright eyes. Anti-reflective coating can address these issues.

Previous designs did not use A/R coating, nor were the principal cellelements optically matched or bonded. This resulted in significanttransmission losses. The present design uses optically index matchedbonding compounds, typically epoxy, to provide improved transmission.

ITO conductive films used as electrodes for the liquid crystal are notcompletely transparent. As part of the pi cell structure 402 these filmsabsorb or reflect some of the incident light. Reflection also occurs atthe optical interface between the ITO and glass substrate, and at theITO and LC interface. The index of refraction of glass is usually givenat 1.5 nominally, while the ITO index value is given as between 1.8 and2.1. This interface will undergo significant reflections with resultinginefficiency and, in addition, some polarization rotation. Indexmatching layers can be added to the ITO to minimize reflections andpolarization artifacts at the interface and also improve transmission.

Transmission can also be improved by using thinner ITO, such as ITOhaving sheet resistivity of around 300 ohms per square. Such an ITOincreases the series resistance of the cell and the need to makeelectrical contacts that are more efficient as described herein withreference to FIGS. 7B and 7C. A number of additional internal opticalinterfaces can have their optical interfaces improved. Glass has anindex of refraction of approximately 1.5, while air is 1.0, and plasticfilms used for polarizer materials may have index of refraction valuesof between 1.4 and 1.6. These interfaces can be index matched either byproviding conventional anti-reflection coatings or by eliminating anyair gap by using a bonding compound with an index of close to 1.5 tominimize the mismatch.

The material chosen for the glass substrate 401 in FIGS. 4A and 4B forthe cell structure has an impact on the overall quality and performanceof the cell. A standard glass used in LC manufacturing, such as waterclear Borofloat, is very good and provides high transmission and lowcoloration. The glass is sufficiently flat over the entire part'ssurface to eliminate significant wavefront distortion. Not using suchmaterials can lead to a lack of clarity of the final projected image inwhich portions of the image may be distorted or have reduced focus.

Polarizer materials generally trade off polarization efficiency fortransmission. An absorption sheet polarizer typically cannot transmitmore than 50 percent of the incident light, and figures in the range of32 to 42 percent are more common with adequate extinctioncharacteristics. For a ZScreen application, the polarizer is typicallyable to withstand high luminous flux, such as on the order of 1,000,000lux. Conventional iodine polarizers tend to overheat and bleach underthis flux. Dyestuff polarizer materials may therefore be employed inorder to withstand higher temperatures without significant damage. Othermaterials may be employed that provide the beneficial aspects disclosedherein.

The polarizer material provides adequate polarization efficiency whilemaximizing transmission. Previous polarizers had transmission of about38 percent and efficiency of 99.9 percent. Dyestuff polarizers willprovide transmission of about 41 percent and efficiency of 99.95percent, providing better performance for both transmission andefficiency while maintaining more stable performance at highertemperatures.

Blanking or the interval between fields is preferably kept to a minimum.The 3D modulation technique previously described projects alternate leftand right eye images in an interleaved triple flash sequence. TheZScreen takes a finite time to switch from one polarization state toanother. During this switching time, the transitional polarization stateis contaminated (compared with the final state), and an image projectedat this time contains polarization states that would be seen by bothleft and right eyes, which is undesirable, so minimum blanking or timeintervals are beneficial.

Switching time of these types of devices has been specified as “10% to90%”, meaning that the time specified is the time required to switchfrom 10% to 90%. The first 10% and last 10% of switching time are thusundefined. Typically in liquid crystal electro-optical devices, theswitching waveform is a stretched into what is termed an “s-shape”,which has long tails—in particular in the last 10% or settling time ofthe waveform. During this settling time, significant light energy of anincomplete polarization state can contribute to crosstalk. Forstereoscopic applications, the switching time is measured from 0% to 99%and from 100% to 1% to more accurately represent the switching timevalue.

To avoid having the image displayed during the switching interval, theimage is blanked, or set to a blank image, during the switching time.The blanking time impacts the brightness of the screen, in that thelonger the blanking time (as a proportion to the total frame time), theless intense the image. The present design employs relatively fastswitching as compared against previously used designs.

Previous designs exhibit a switching time of approximately 2milliseconds (100% to 1%). Improvements in drive circuits (using thequenching pulse waveform as described above) and reducing the liquidcrystal gap thickness can result in a switching time of less than 600microseconds. The liquid crystal material used to fill the cell isusually a mixture of several kinds of materials blended to create thebest possible trade offs in terms of performance. Enhancements to thespeed of the push-pull device result from these improvements.

A circular polarized system has circularly polarized light that exitsthe ZScreen, circularly polarized for one wavelength and ellipticallypolarized for all other wavelengths in the visible spectrum. Forefficient modulation, the analyzers (glasses) of the circular polarizedsystem are an inverse of the polarizer. The analyzers analyze circularpolarization at the wavelength that the polarizer creates circular, andanalyze the correct degree of ellipticity everywhere else.

To achieve the high quality viewing characteristics, the wavelength forcircular polarization states matches the ZScreen and the viewer'sglasses. Retardances at other wavelengths are preferably a close match,and the efficiency of linear polarization is preferably high. The effectof retardance mismatch in these elements is that light leaks through thepolarizers when in a crossed state. Leakage is usually higher in red andblue. The wavelength of circular polarization is relatively low in thevisible spectrum, in the present arrangement approximately 525 nm. Sucha wavelength visually balances the leakage of red and blue to minimizethe visual effect, and provide as neutral a color for the resultingleakage as possible.

Thermal/Flux Management

The ZScreen design taught herein can withstand a high level of luminousenergy from the projector. The projector provides upwards of 25000lumens, and future projectors may provide more luminous energy. 25000lumens is approximately 60 watts of radiant power. Approximately 36watts are dissipated on the ZScreen as a result of absorption in theglass and the linear polarizer. This results in a rise in temperature,with potential damaging effects to the polarizer. This much power maytake the liquid crystal to an isotropic phase, where the liquid crystalfails to provide any modulation.

The present design addresses these issues by increasing the active areaof the ZScreen by a factor of more than double, to providing a largerarea for dissipating the heat, (fewer watts per square inch) and byproviding a cooling fan to circulate cool air across the polarizersurface.

The cinema system, using a projector such as DLP Cinema™ from TexasInstruments provides accurate color calibration in the projector so thatevery theatre has the same color balance. The calibration is usuallyperformed by measuring the color characteristics of the system. Thesystem projects through the port glass as usual and the user/viewerobserves the image, reflected off the theatre screen, through the 3-Dglasses. Color correction in the system makes the correct shade of whiteand each of the RGB primary colors when seen by the eye. Calibrationinvolves turning down the luminance of one or more of the RGB channelswithin the projector, resulting in lower light output. System efficiencycan be maximized if the impact of all system components combined resultsin a relatively small amount of correction in the projector. The presentdesign uses the bluish color of the projection screen to balance out theyellow-green color imparted by the ZScreen in combination with theglasses worn by the user/viewer, resulting in minimal color correctionrequired in the projector and maximizing light output.

The result of the presently disclosed improvements to the push-pullelectro-optical ZScreen modulator and the stereoscopic projection systemhas been to substantially improve the image quality of stereoscopicmovies in theatrical cinemas. These stereoscopic motion pictures havesuperior left and right channel isolation and are clearer and brighterthan previous designs.

In general, the present design results in a faster switching speed,enhanced transmission qualities, better extinction ratios, and enhancedthermal and flux management. Faster switching speeds are attained byusing the enhanced drive scheme, enhancing the LC material and reducingthe gap, and changing the connection to reduce series resistance,resulting in a switching speed decrease of approximately 33 percent incertain applications. Transmission may be improved on the order of 33percent in some instances by using the AR coating described, ITO indexmatch, bonding air to material components, using clearer/flatter glass,using a less dense polarizer, and reducing projector blanking time. Theextinction ratio can be improved from the 60:1 rate seen previously toon the order of 250:1 using the enhanced LC material, matching theeyewear polarizer to the ZScreen, using AR coating and bonding air tomaterial components. Thermal and flux management may be achieved usingdyestuff polarizer, increasing area, and employing a cooling fan. Use ofeach of these improvements can increase viewing experiencessignificantly, while employing all of these improvements collectivelycan provide a highly superior design.

The design presented herein and the specific aspects illustrated aremeant not to be limiting, but may include alternate components whilestill incorporating the teachings and benefits of the invention, namelythe improved push-pull electro-optical ZScreen modulator and thestereoscopic projection system. While the invention has thus beendescribed in connection with specific embodiments thereof, it will beunderstood that the invention is capable of further modifications. Thisapplication is intended to cover any variations, uses or adaptations ofthe invention following, in general, the principles of the invention,and including such departures from the present disclosure as come withinknown and customary practice within the art to which the inventionpertains.

The foregoing description of specific embodiments reveals the generalnature of the disclosure sufficiently that others can, by applyingcurrent knowledge, readily modify and/or adapt the system and method forvarious applications without departing from the general concept.Therefore, such adaptations and modifications are within the meaning andrange of equivalents of the disclosed embodiments. The phraseology orterminology employed herein is for the purpose of description and not oflimitation.

1. A method of displaying a stereoscopic video image, comprising:positioning a polarization modulator so that light comprising thestereoscopic video image propagates therethrough; and driving thepolarization modulator in synchronization with fields of a fieldsequential image so that a transmitted image emerging from thepolarization modulator consists of right-handed circularly polarizedfields alternating at field rate with left-handed circularly polarizedfields; wherein said driving comprises moving an electrical charge usinga waveform comprising at least one quenching pulse in association with aholding voltage comprising a relatively brief voltage spike opposite inpolarity to the holding voltage at a beginning of a holding voltageperiod.
 2. The method of claim 1, further comprising positioning aleft-handed circular polarizer analyzer and a right-handed circularpolarizer analyzer so that circularly polarized light emerging from thepolarization modulator propagates through space and is reflected by apolarizing conserving screen through space and then through one circularpolarizer analyzer while being blocked by a complementary circularpolarizer analyzer.
 3. The method of claim 1, wherein the polarizationmodulator comprises a first surface mode liquid crystal cell and asecond surface mode liquid crystal cell, and wherein the first cell isdriven by a first voltage signal that alternates at field rate between alow voltage square wave and a high voltage square wave, and the secondcell is driven by a second voltage signal having substantially the sameamplitude as the first voltage signal but having phase opposite to thefirst signal's phase.
 4. The method of claim 1, wherein each fieldincludes at least two subfields, each subfield having a duration, thepolarization modulator includes a first surface mode liquid crystal celland a second surface mode liquid crystal cell, and including: drivingthe first cell with a first voltage signal; and driving the second cellwith a second voltage signal, in such a manner that the absolutemagnitude of the envelope of the first voltage signal and the absolutemagnitude of the envelope of the second voltage signal decreasesubstantially simultaneously during each subfield.
 5. The method ofclaim 1, wherein each field includes at least two subfields, and eachsubfield having a duration, the polarization modulator includes a firstsurface mode liquid crystal cell and a second surface mode liquidcrystal cell, and comprising: driving the first cell with a firstcarrier-less voltage signal; and driving the second cell with a secondcarrier-less voltage signal, in such a manner that the absolutemagnitude of the first voltage signal and the absolute magnitude of thesecond voltage signal decrease substantially simultaneously during eachsubfield.
 6. The method of claim 1, wherein the polarization modulatorincludes a first surface mode liquid crystal cell and a second surfacemode liquid crystal cell, and wherein the first cell is driven by afirst voltage signal that alternates at field rate between a low ACvoltage portion and a high AC voltage portion, and the second cell isdriven by a second voltage signal having substantially the sameamplitude as the first voltage signal but having phase opposite to thefirst signal's phase.
 7. The method of claim 6, wherein each of the ACvoltage portions is a 2 KHz sinusoidal wave, the low AC voltage portionhas peak to peak amplitude in the range from zero volts to ten volts,and the high AC voltage portion has peak to peak amplitude in the rangefrom 40 volts to 80 volts.
 8. The method of claim 1, wherein thepolarization modulator comprises a push-pull modulator.
 9. The method ofclaim 1, wherein the polarization modulator comprises a dyestuffpolarizer.
 10. The method of claim 1, wherein the polarization modulatorcomprises a wire grid polarizer.
 11. The method of claim 1, wherein thepolarization modulator has air to material surfaces bonded.
 12. Themethod of claim 1, wherein polarization modulator comprises a liquidcrystal cell having water clear Borofloat.
 13. The method of claim 1,wherein the polarization modulator is employed in connection with ascreen, and persons viewing the screen employ eyewear comprisingpolarizing elements matched to the polarization modulator.
 14. A methodof displaying a stereoscopic video image, comprising: driving apolarization modulator so that light comprising the stereoscopic videoimage propagates therethrough; wherein said driving occurs insynchronization with fields of a field sequential image so that atransmitted image emerging from the polarization modulator comprisesright-handed circularly polarized fields alternating at field rate withleft-handed circularly polarized fields; and further wherein saiddriving comprises moving an electrical charge using a waveformcomprising at least one quenching pulse in association with a holdingvoltage comprising a relatively brief voltage spike opposite in polarityto the holding voltage at a beginning of a holding voltage period. 15.The method of claim 14, further comprising positioning a left-handedcircular polarizer analyzer and a right-handed circular polarizeranalyzer so that circularly polarized light emerging from thepolarization modulator propagates through space and is reflected by apolarizing conserving screen through space and then through one circularpolarizer analyzer while being blocked by a complementary circularpolarizer analyzer.
 16. The method of claim 14, wherein the polarizationmodulator comprises a first surface mode liquid crystal cell and asecond surface mode liquid crystal cell, and wherein the first cell isdriven by a first voltage signal that alternates at field rate between alow voltage square wave and a high voltage square wave, and the secondcell is driven by a second voltage signal having substantially the sameamplitude as the first voltage signal but having phase opposite to thefirst signal's phase.
 17. The method of claim 14, wherein each fieldincludes at least two subfields, each subfield having a duration, thepolarization modulator includes a first surface mode liquid crystal celland a second surface mode liquid crystal cell, and including: drivingthe first cell with a first voltage signal; and driving the second cellwith a second voltage signal, in such a manner that the absolutemagnitude of the envelope of the first voltage signal and the absolutemagnitude of the envelope of the second voltage signal decreasesubstantially simultaneously during each subfield.
 18. The method ofclaim 14, wherein each field includes at least two subfields, and eachsubfield having a duration, the polarization modulator includes a firstsurface mode liquid crystal cell and a second surface mode liquidcrystal cell, and comprising: driving the first cell with a firstcarrier-less voltage signal; and driving the second cell with a secondcarrier-less voltage signal, in such a manner that the absolutemagnitude of the first voltage signal and the absolute magnitude of thesecond voltage signal decrease substantially simultaneously during eachsubfield.
 19. The method of claim 14, wherein the polarization modulatorincludes a first surface mode liquid crystal cell and a second surfacemode liquid crystal cell, and wherein the first cell is driven by afirst voltage signal that alternates at field rate between a low ACvoltage portion and a high AC voltage portion, and the second cell isdriven by a second voltage signal having substantially the sameamplitude as the first voltage signal but having phase opposite to thefirst signal's phase.
 20. The method of claim 19, wherein each of the ACvoltage portions is a 2 KHz sinusoidal wave, the low AC voltage portionhas peak to peak amplitude in the range from zero volts to ten volts,and the high AC voltage portion has peak to peak amplitude in the rangefrom 40 volts to 80 volts.
 21. The method of claim 14, wherein thepolarization modulator comprises a dyestuff polarizer.
 22. The method ofclaim 14, wherein the polarization modulator has air to materialsurfaces bonded.
 23. The method of claim 14, wherein liquid crystal usedin the polarization modulator comprises water clear Borofloat.
 24. Themethod of claim 14, wherein the polarization modulator is employed inconnection with a screen, and persons viewing the screen employ eyewearcomprising polarizing elements matched to the polarization modulator.25. A stereoscopic video image display system, comprising: apolarization modulator positioned so that a stereoscopic imagepropagates therethrough; wherein said polarization modulator is drivenin synchronization with fields of a field sequential image so that atransmitted image emerging from the polarization modulator comprisesright-handed circularly polarized fields alternating at field rate withleft-handed circularly polarized fields; and further wherein saidpolarization modulator is driven by moving an electrical charge using awaveform comprising at least one quenching pulse in association with aholding voltage comprising a relatively brief voltage spike opposite inpolarity to the holding voltage at a beginning of a holding voltageperiod.
 26. The system of claim 25, wherein the polarization modulatorcomprises a first surface mode liquid crystal cell and a second surfacemode liquid crystal cell, and wherein the first cell is driven by afirst voltage signal that alternates at field rate between a low voltagesquare wave and a high voltage square wave, and the second cell isdriven by a second voltage signal having substantially the sameamplitude as the first voltage signal but having phase opposite to thefirst signal's phase.
 27. The system of claim 25, wherein thepolarization modulator includes a first surface mode liquid crystal celland a second surface mode liquid crystal cell, and wherein the firstcell is driven by a first voltage signal that alternates at field ratebetween a low AC voltage portion and a high AC voltage portion, and thesecond cell is driven by a second voltage signal having substantiallythe same amplitude as the first voltage signal but having phase oppositeto the first signal's phase.
 28. The system of claim 25, wherein thepolarization modulator comprises a push-pull modulator.
 29. The systemof claim 25, wherein the polarization modulator comprises a dyestuffpolarizer.
 30. The system of claim 25, wherein the polarizationmodulator comprises a wire grid polarizer.
 31. The system of claim 25,wherein the polarization modulator has air to material surfaces bonded.32. The system of claim 25, wherein polarization modulator comprises aliquid crystal cell having water clear Borofloat.
 33. The system ofclaim 25, wherein the polarization modulator is employed in connectionwith a screen, and persons viewing the screen employ eyewear comprisingpolarizing elements matched to the polarization modulator.